1. Field of the Invention
The present invention relates to a chain guide of a straddle type all terrain vehicle (ATV).
2. Related Art
There is known a looped-over power transmission device using a drive chain as means for transmitting power of an engine to driving wheels (e.g., rear wheels). The looped-over power transmission device is formed by looping the drive chain over between a drive sprocket on an engine side and a driven sprocket on a driving wheel side, and such power transmission device is used in many kinds of vehicles.
Incidentally, the drive chain may elongate during use. The looped-over power transmission device using the drive chain includes a tension side on which the drive chain is stretched to transmit power and a slack side on which the drive chain circulates depending on a power transmitting direction.
On the tension side of the drive chain, tension is always applied, and therefore, a skip does not occur. However, the slack-side drive chain suddenly turns in direction at a portion where the chain is engaged with the driven sprocket, and therefore, the chain may lift outward in a radial direction of the sprocket in a waving manner under the influence of an inertial force and a part of the chain may be disengaged from the sprocket in some cases. Especially, when a transmission load suddenly increases or decreases under the influence of abrupt acceleration of the vehicle or a condition of a road surface, the tension-side drive chain elongates and contracts, and strength of the slack side changes to cause a flutter of the chain to thereby further encourage the skip phenomenon.
Therefore, in order to prevent such a skip of the drive chain, a protector may be disposed at a regular distance from an outer periphery of a sprocket as shown, for example, in Japanese Utility Model Application Publication No. 57-24620.
In a case of a vehicle such as a straddle type all terrain vehicle intended for traveling on a muddy ground or a rough road that is not leveled, wear of links and coupling pins develops and thereby reduces durability when mud or muddy water sticks to the drive chain for transmitting power of the engine to the rear wheels. The whole drive chain is covered with a chain cover to avoid such adverse phenomenon.
However, if the driven sprocket is displaced to adjust the tension in the drive chain suffering the elongation during the use as described above, complicated operation such as removal and moving of the chain cover is required. Similarly, it is required to move or adjust the protector for preventing the skip of the drive chain, further complicating the operation.